Hi,
Well, this sounds very irritating and annoying. The fact that you have always had eczema means you will most likely know its cause it usually attributed to some combination of environmental and genetic causes. It's certainly the case that under conditions of stress people with eczema can experience flares and there are indications that stress management techniques such as relaxation and cognitive behavior therapy can help.
An allergy however is a specific reaction to an allergen, which can be almost anything. One of the reactions to allergies is itchy skin rash - which is what you are experiencing. I wonder if you have any other allergy symptoms like sneezing, wheezing, coughing, itchy eyes?
You feel that you are allergic to everything which probably means a little detective work is needed on your part to rule things in and out. There is also some great information and advice on MyAllergyNetwork.com.